Planetary protection implementation on Mars Reconnaissance Orbiter mission Original Research Article

In August 2005 NASA launched a large orbiting science observatory, the Mars Reconnaissance Orbiter (MRO), for what is scheduled to be a 5.4-year mission. High resolution imaging of the surface is a principal goal of the mission. One consequence of this goal however is the need for a low science orbit. Unfortunately this orbit fails the required 20-year orbit life set in NASA Planetary Protection (PP) requirements [NASA. Planetary protection provisions for robotic extraterrestrial missions, NASA procedural requirements NPR 8020.12C, NASA HQ, Washington, DC, April 2005.]. So rather than sacrifice the science goals of the mission by raising the science orbit, the MRO Project chose to be the first orbiter to pursue the bio-burden reduction approach. Cleaning alone for a large orbiter like MRO is insufficient to achieve the bio-burden threshold requirement in NASA PP requirements. The burden requirement for an orbiter includes spores encapsulated in non-metallic materials and trapped in joints, as well as located on all internal and external surfaces (the total spore burden). Total burden estimates are dominated by the mated and encapsulated burden. The encapsulated burden cannot be cleaned. The total burden of a smaller orbiter (e.g., Mars Odyssey) likely could not have met the requirement by cleaning; for the large MRO it is clearly impossible. Of course, a system-level partial sterilization, with its attendant costs and system design issues, could have been employed. In the approach taken by the MRO Project, hardware which will burn up (completely vaporize or ablate) before reaching the surface or will at least attain high temperature (500 °C for 0.5 s or more) due to entry heating was exempt from burden accounting. Thus the bio-burden estimate was reduced. Lockheed Martin engineers developed a process to perform what is called breakup and burn-up (B&B) analysis. The use of the B&B analysis to comply with the spore burden requirement is the main subject of this article. However, several components aboard the orbiter were predicted to fail the minimum time at temperature requirements (or could not conservatively be shown to meet the conditions). An implementation plan was generated to address the highest contributors to the bio-burden assessment that fail to meet the requirements. The spore burden for these components was estimated by direct and proxy burden assays, NASA PP specifications, and dry heat microbial reduction, as appropriate. Items on the orbiter that required rework during assembly were also individually assessed. MRO met the spore burden requirement based on the B&B analysis, the MRO Planetary Protection Implementation Plan, and verification by the NASA Planetary Protection Officer’s (PPO) independent assays. The compliance was documented in the MRO PP Pre-Launch Report. MRO was approved for flight by the NASA PPO.